According to Buddhism, kamma, good and bad, is in the intention. An example is given in the Tipitaka of a monk unintentionally sitting on small child and the child died. It is said that the first precept has not been broken, that the monk is not guilty of killing, but only of incautious sitting. A person can incautiously sit on chair whether there is a child there or not, even though the child has died, the only thing monk has done bad is incautiously sit.

Having that in mind, it would seem that there is no place in Buddhism for environmentalist concerns. People who pollute the Earth and thereby destroy the health and lives of countless people and basically threaten the survival of humans on this planet- do not do so intentionally, so, if I am understanding this right, according to Buddhism they are not doing anything really that much bad.

In a way that would be true. If one doesn't intentionally hurt others there is no wrongdoing. However, that's not where Buddhism ends. After avoiding the 'bad', it is also important to cultivate the good. As a famous saying goes:

"To avoid all evil, to cultivate good, and to purify one's mind—this is the teaching of the Buddhas"

It starts with avoiding 'evil'. For most people that is already hard enough. But then it also says cultivate good. So for example first we abstain from stealing (the 'bad'), then we cultivate sharing and giving away (the 'good'). First we abstain from lies, then we cultivate kind speech that connects people.

So when looking at environmental issues, while it wouldn't be bad per se to unintentionally pollute the environment, it would be a training of cultivating good to have concern for other future living beings. So you will generally find Buddhists are very concerned about environmental topics. Many are also vegetarian for example, or monasteries and temples ask you to take in mind the environment when using the showers etc.

I wouldn't say it is part of the precepts as the Buddha put them down - not the basic 5 at least, since those mainly have to do with the internal world of the mind. I know there are some things you could say are connected with this in the monks & nuns precepts, like not destroying plants. But of course in the time of the Buddha 2500 years ago, environmental issues were not really there, so we can't expect to find those things in those teachings. There is a modernization of the precepts by Thich Nhat Hahn which however reflects an attitude like this which I think is worth reflecting on:

Reverence For LifeAware of the suffering caused by the destruction of life, I am committed to cultivating the insight of interbeing and compassion and learning ways to protect the lives of people, animals, plants, and minerals. I am determined not to kill, not to let others kill, and not to support any act of killing in the world, in my thinking, or in my way of life. Seeing that harmful actions arise from anger, fear, greed, and intolerance, which in turn come from dualistic and discriminative thinking, I will cultivate openness, non-discrimination, and non-attachment to views in order to transform violence, fanaticism, and dogmatism in myself and in the world.

True HappinessAware of the suffering caused by exploitation, social injustice, stealing, and oppression, I am committed to practicing generosity in my thinking, speaking, and acting. I am determined not to steal and not to possess anything that should belong to others; and I will share my time, energy, and material resources with those who are in need. I will practice looking deeply to see that the happiness and suffering of others are not separate from my own happiness and suffering; that true happiness is not possible without understanding and compassion; and that running after wealth, fame, power and sensual pleasures can bring much suffering and despair. I am aware that happiness depends on my mental attitude and not on external conditions, and that I can live happily in the present moment simply by remembering that I already have more than enough conditions to be happy. I am committed to practicing Right Livelihood so that I can help reduce the suffering of living beings on Earth and reverse the process of global warming.

In my eyes, however, it can become a sort of trap when we think Buddhism is meant to make the world one harmonious and healthy place. Some Buddhists seem to have this ideal picture, but obviously it won't happen. For me Buddhism is mainly about ending the process of suffering we create for ourselves.

greenjuice wrote:Could maybe environmental concern be considered like a part of Buddha's precepts that one should protect one's family and friends, like those found in the Sigala Sutta?

Also, is 'doing good' that comes after 'not doing bad' in Buddhism considered, to use a Christian term, supererogatory?

I don't know what supererogatory is, so I can't answer the second question. But the idea of good and bad in Buddhism is different from Christianity in that it is not a judgment, but more like, what is good will benefit people and what is bad will work against them.

reflection wrote:I wouldn't say it is part of the precepts as the Buddha put them down - not the basic 5 at least, since those mainly have to do with the internal world of the mind.

I wasn't talking about the five precepts, but about other Buddha's rules/ advice, like when in the Sigala Sutta he talkes about protecting your family and friends, and in Dighajanu Sutta when he talks about protective efforts against theft and disaster.

I don't know what supererogatory is

Good, but unnecessary, additional. E.g. among ancient Greeks the academics thought that charity is supererogatory, it is something good to do, but not a necessary condition to being a good person, you can avoid doing it, and there's nothing wrong with that- whereas the stoics thought that charity and helping others in general is not supererogatory but necessary, and that if you don't practice it- you cannot be a good person, if you can but don't it you are unjust. Similar differences concerning charity and also other topics exist among Christian and Muslim denominations.

reflection wrote:I wouldn't say it is part of the precepts as the Buddha put them down - not the basic 5 at least, since those mainly have to do with the internal world of the mind.

I wasn't talking about the five precepts, but about other Buddha's rules/ advice, like when in the Sigala Sutta he talkes about protecting your family and friends, and in Dighajanu Sutta when he talks about protective efforts against theft and disaster.

I don't know what supererogatory is

Good, but unnecessary, additional. E.g. among ancient Greeks the academics thought that charity is supererogatory, it is something good to do, but not a necessary condition to being a good person, you can avoid doing it, and there's nothing wrong with that- whereas the stoics thought that charity and helping others in general is not supererogatory but necessary, and that if you don't practice it- you cannot be a good person, if you can but don't it you are unjust. Similar differences concerning charity and also other topics exist among Christian and Muslim denominations.

As for the first part, you've already had some good answers but I would start with the cultivation of compassion for all living things. Extending compassion beyond ourselves and our family to other people leads pretty quickly to a push for social justice, and extending it to other species leads pretty quickly to concern for the environment.